CN112601885B

CN112601885B - Method for operating an internal combustion engine system

Info

Publication number: CN112601885B
Application number: CN201880096838.1A
Authority: CN
Inventors: 弗雷德里克·拉姆; 约翰·卡伦安德松
Original assignee: Volvo Truck Corp
Current assignee: Volvo Truck Corp
Priority date: 2018-08-23
Filing date: 2018-08-23
Publication date: 2023-05-26
Anticipated expiration: 2038-08-23
Also published as: EP3841289A1; CN112601885A; US11346309B2; US20210180533A1; WO2020038576A1; EP3841289B1

Abstract

The invention relates to a method for operating an internal combustion engine system (2), wherein the internal combustion engine system (2) is provided with an inlet line (3), an exhaust line (4) and an Exhaust Gas Recirculation (EGR) system (5), wherein the EGR system (5) comprises an EGR conduit (6) which fluidly connects the exhaust line (4) and the inlet line (3), and wherein a gas feed device (7) is arranged in the EGR conduit (6) which is configured to feed exhaust gas from the exhaust line (4) to the inlet line (3). The method is characterized in that it comprises the following steps: an indication of accumulated deposits of soot, hydrocarbons or other contaminants in the gas feed device (7) is detected by determining whether a rotational friction force of a rotating member (71, 72) of the gas feed device (7) exceeds a threshold value. The invention also relates to an internal combustion engine system (2) configured to be operated by such a method, and a vehicle (1) provided with such an engine system (2). The invention also relates to a device for controlling the above method.

Description

Method for operating an internal combustion engine system

Technical Field

The present invention relates to a method for operating an internal combustion engine system, which is provided with an EGR system and a gas feed for feeding exhaust gases in the EGR system, for example. The invention also relates to an internal combustion engine system, a vehicle and a control device for controlling the above method.

The invention is generally applicable to heavy vehicles such as trucks, buses and construction equipment, but is also applicable to other types of applications as well as to other types of vehicles and vessels. Although the invention will be described with respect to a truck, the invention is not limited to this particular vehicle.

Background

EGR (exhaust gas recirculation) is a well-known means for reducing the amount of nitrogen oxides (NOx) in the exhaust gas of an internal combustion engine, for example a diesel engine arranged for propelling a vehicle such as a truck. A portion of the exhaust gas is recirculated to the intake side of the engine, which reduces the maximum combustion temperature in the engine and reduces NOx production.

The EGR system may be arranged in different ways but includes at least some form of EGR passage that fluidly connects the exhaust side and the intake side of the engine. Typically, an EGR system includes an EGR flow control valve and an EGR cooler.

Control of EGR flow in an EGR system is associated with various challenges such as fluctuating intake and exhaust pressures, hardware durability issues due to high exhaust temperatures and soot deposition, condensation and corrosion in the EGR cooler, and the like. Further challenges are: under certain operating conditions in many engine systems, and during most of the time for certain engine systems provided with high efficiency turbine devices, the pressure on the intake side is higher than the pressure on the exhaust side, so there is no driving force for recirculating the exhaust.

To overcome the challenges associated with "pressure on the intake side is higher than pressure on the exhaust side", US6435166 proposes the use of a gas feeder (EGR pump/compressor) to feed gas from the exhaust side to the intake side. While such a gas feeder appears to solve the expected problem, such a solution is rare on commercial engines, possibly due to durability issues.

An alternative approach to handling the higher pressure on the intake side is to use a Variable Geometry Turbine (VGT) device to control the exhaust pressure (i.e., to keep the exhaust pressure high enough). A disadvantage of such VGT devices is the fuel consumption penalty (fuel consumption penalty) associated with increased exhaust back pressure. Another approach is to supply EGR into the intake conduit via a venturi nozzle. A disadvantage of venturi tubes is that they are generally associated with a significant reduction in pressure, particularly for large flows of gas. Yet another approach is to create pulsed EGR flow by placing a check valve in the EGR conduit that provides flow to the intake side each time an exhaust pulse occurs, but wherein backflow between pulses is prevented. A disadvantage associated with pulsed EGR flow is the difficulty in controlling flow.

Thus, there is a need for an EGR system that also provides efficient and reliable exhaust gas recirculation when the pressure on the intake side is higher than the pressure on the exhaust side.

Disclosure of Invention

It is an object of the present invention to provide a method and arrangement which provides a more efficient and reliable recirculation of exhaust gases in an internal combustion engine system when the pressure on the inlet side is higher than the pressure on the exhaust side than in known methods and arrangements.

According to a first aspect of the invention, this object is achieved by a method as described below. According to a second aspect of the invention, this object is achieved by a device (engine system and vehicle) as described below. According to a further aspect of the invention, the object is achieved by a computer related product/medium or a control unit for controlling the method.

The method relates to a method for operating an internal combustion engine system, wherein the internal combustion engine system is provided with an intake conduit, an exhaust conduit and an Exhaust Gas Recirculation (EGR) system, wherein the EGR system comprises an EGR conduit fluidly connecting the exhaust conduit and the intake conduit, and wherein a gas feed device is arranged in the EGR conduit, the gas feed device being configured to feed exhaust gas from the exhaust conduit to the intake conduit.

The method is characterized in that it comprises the following steps: an indication of accumulated deposits of soot, hydrocarbons, or other contaminants in the gas feed device is detected by determining whether a rotational friction of a rotating member of the gas feed device exceeds a threshold value.

Typically, during operation of the engine system, various materials will gradually accumulate in the gap between the rotating member and the stationary portion of the gas feed apparatus. The gas feed means may be, for example, a positive displacement pump of the Roots blower type having a pair of rotors provided with meshing lobes, with a small gap between the lobes and the peripheral housing. As the gap begins to close with deposited material, it will gradually increase the rotational friction of the rotating member. At some point in time, or directly at start-up (if the rotating member has stuck), the rotational friction will be above a threshold. Thus, the method provides an indication as to whether the gas feed needs to be cleaned or otherwise fails to function as intended. As further described below, where such an indication is provided, there are various options available, such as rotating the rotating member back and forth, cleaning the gas feed with a flushing liquid, or bypassing the gas feed to allow continued operation of the engine system even if the gas feed has become stuck or otherwise inoperable.

Thus, the method provides for efficient and reliable recirculation of exhaust gases, in particular in an internal combustion engine system where the pressure on the intake side is higher than the pressure on the exhaust side, as the method provides an indication of various durability problems in connection with a gas feed for feeding recirculated exhaust gases; thus, the method provides the possibility to eliminate, reduce or in some other way deal with such problems at an early stage. Briefly, the method makes an EGR gas feed apparatus useful for commercial engines.

The method may be performed during normal operation of the engine system, during start-up (cold start) of the engine system, or when "engine components" (pistons, valves, turbine devices, etc.) of the engine system are not running.

The gas feed may include one or more rotating members and the rotational friction of the one or more rotating members may be determined.

In one embodiment, the determination of the rotational friction includes one or more of the following steps:

-measuring the torque applied to the rotating member;

measuring a driving power of a driving source, such as a current of a driving motor, arranged to drive the gas feeding means and rotate the rotating member;

-measuring the actual rotational speed of the rotating member; and/or

-measuring the response time of the rotating member between the change in driving power and the resulting change in rotational speed.

Thus, the rotational friction can be determined indirectly from different measurements and calculations, and combinations thereof.

In one embodiment, in the event that an indication of accumulated deposits is detected, the method further comprises the steps of: the rotating member is operated in a reverse rotational direction opposite to the rotational direction used under normal operating conditions. Changing the direction of rotation can loosen the deposit from the gas feed.

In one embodiment, the rotating member is operated in the reverse rotation direction in a pulsed manner for a short period of time, wherein the pulsed reverse operation is followed by continued operation in the normal operation rotation direction. First, it is often sufficient to operate the rotating member in the reverse direction for only a short period of time to remove the deposits. Second, reversing the direction only for a short period of time does not have any significant effect on the normal operation of the engine system (i.e., in the case where the engine system is in normal operation; the gas feed apparatus may also be operated in any direction when the engine system is not in normal operation and no exhaust gas or the like is produced). Preferably, the short period of time for which the rotating member is operated in the reverse direction is less than 10s, preferably less than 5s. The step of pulsing the rotating member in the reverse rotation direction may be repeated. Alternatively or in combination, the method may comprise the steps of: the rotating member is alternately operated in a reverse rotation direction and a normal rotation direction in a pulse manner. This includes various variants: wherein the rotating member is run twice or more in succession in the same direction before changing direction.

In one embodiment, in the event that an indication of accumulated deposits is detected, the method further comprises the steps of: the driving power of the driving motor arranged to drive the gas feeding means and the rotating member is increased to a power level higher than the power level used under normal operating conditions. This may lead to loosening of the deposit and may be used in combination with or instead of running the rotating member in the reverse direction.

In one embodiment, in the event that an indication of accumulated deposits is detected, the method further comprises the steps of: the exhaust gas flow in the EGR conduit is led into a bypass conduit arranged in fluid communication with the EGR conduit upstream and downstream of the gas feed. This may be used as an emergency solution when the rotating member has become stuck or the gas feeding device is totally inoperative for other reasons. Thus, the engine system can still be operated, so the vehicle can still be used and no immediate traction/rescue is required. An engine break (or variable geometry turbine) may be arranged to increase the pressure in the exhaust duct to provide drive for EGR flow without a gas feed. An intake throttle may also be used to provide EGR actuation.

In one embodiment, in the event that an indication of accumulated deposits is detected, the method further comprises the steps of: the temperature of the exhaust gas flowing through the gas feed is increased. This is useful for burning out hydrocarbons (fuel and oil residues) that have accumulated in the gas feed as much as possible. In order to remove hydrocarbons efficiently, the temperature of the exhaust gas in the EGR conduit may be raised to about 120 ℃ or even up to about 150 ℃.

In order to raise the temperature of the exhaust gas flowing through the gas feed, the method may comprise the steps of: the internal combustion engine system is operated in order to raise the temperature of the exhaust gases and/or to reduce the cooling effect of an EGR cooler device arranged in an EGR conduit upstream of the gas feed. Reducing the cooling effect of the EGR cooler device comprises, for example, switching off the cooler and using an EGR cooler bypass passage.

In one embodiment, in the event that an indication of accumulated deposits is detected, the method further comprises the steps of: flushing liquid is provided in the EGR conduit upstream of the gas feed in order to flush and clean the gas feed. Thus, the flushing liquid/washing liquid will follow the EGR flow towards and into the gas feed means, where it will clean the gas feed means by removing soot and other accumulated deposits from the parts of the gas feed means that are in contact with the EGR flow during operation of the engine system. Such rinsing/cleaning may be used in combination with rotating the rotating member back and forth and other measures as described above.

In addition to the potential for such flushing/cleaning to remove accumulated deposits that lead to an increase in the rotational friction of the rotating member, it also protects the function of the gas feed and reduces its risk of sticking etc., and also serves to reduce performance variations and allows for the use of smaller tolerances that may be used to increase the efficiency of the gas feed, for example in positive displacement pumps of the Roots blower type. Thus, the rinsing/cleaning operation may also be performed without the aforementioned step of detecting any indication of accumulated deposits; rinsing/cleaning may be performed conventionally and/or for preventive purposes to prevent substantial accumulation of deposits.

Providing liquid in the EGR conduit is contradictory to the conventional protection of the EGR system, as measures are generally taken to avoid introducing or generating (condensing) liquid in the EGR system, which may lead to corrosion or other damage. In addition, as a precaution, it is also generally avoided to provide liquid in the conduit upstream of the feeding means intended to feed gas rather than liquid.

Typically, the rinse liquid is water or a water-based liquid, but may also be, for example, an alcohol or alcohol-water mixture or other type of liquid, which may be stored in a separate tank. In principle, a portion of the flushing liquid introduced into the EGR duct may be in gaseous form before and/or during the introduction, which may be, for example, steam, but when the flushing liquid/fluid is in contact with the gas feed, the flushing liquid/fluid should be in liquid form in order to exhibit a more efficient cleaning performance. It may be more efficient to use flushing liquid that is also in liquid form before and during introduction into the EGR duct.

The amount of flushing liquid used in one flushing/cleaning step may vary and may be adapted to, for example, the size of the EGR conduit (which in turn may depend on the size of the engine), the current and earlier operating conditions of the engine, and the time elapsed since the last flushing operation. The flushing operation may be allowed to continue for a period of time and may be repeated.

In one embodiment, the method further comprises the steps of: the exhaust gas is condensed in or downstream of an EGR cooler arranged in connection with the EGR conduit so as to form an EGR condensate, and the EGR condensate is used as flushing liquid. This is an efficient way of providing flushing liquid, since in any case an EGR cooler is included in the system, which is able to normally produce condensate. If the EGR cooling device is arranged upstream of the EGR gas feed device, exhaust gases condensed in the cooling device or in a conduit between the cooling device and the gas feed device are thus provided upstream of the gas feed device. In this case, no additional hardware is required. However, the EGR duct may be designed to have a special effect on the condensation, for example by forming passages or the like that enhance the condensation at certain locations. If the cooling device is arranged downstream of the gas feed device, a channel (and a valve) may be arranged for guiding condensate back into the EGR duct upstream of the gas feed device. Regardless of the relative flow sequence of the cooling device and the gas feed device, some type of tank may be arranged to accumulate condensed exhaust gas and form a rinse liquid supply. A passage may be arranged to lead condensate from such a reservoir in a controllable manner to the inlet of the EGR conduit upstream of the EGR gas feed.

Engine systems are typically operated to avoid or minimize condensation in EGR. In one embodiment, the engine system is controlled to produce (more) EGR condensate than during normal operation, if desired, for example, by: i) Operating the EGR cooler device at high efficiency (by increasing the mass flow rate of the cooling medium and/or decreasing the temperature of the cooling medium); ii) increasing the EGR mass flow (which results in a greater amount of water in the EGR flow and thus a higher rate of condensate production), iii) increasing the fuel ratio in the air-fuel mixture combusted in the engine so as to produce exhaust gas with a higher concentration of water (e.g., by controlling the intake throttle to reduce the amount of air), and/or iv) operating the EGR system while the engine is cold (i.e., below normal operating temperature) so that the exhaust gas is also "cold" and more prone to efficient condensation.

In one embodiment, the step of providing flushing liquid in the EGR conduit upstream of the EGR gas feed means comprises the steps of: at least a portion of the flushing fluid is introduced into the EGR conduit via a flushing fluid channel arranged in fluid communication with the flushing fluid tank and the EGR conduit. This is an alternative or complement to the step of providing flushing fluid by directly condensing EGR in the EGR conduit. The liquid contained in the flushing tank may be EGR condensate or another liquid that has previously accumulated, or a mixture of EGR condensate and another liquid.

In one embodiment, the step of providing a flushing fluid in the EGR conduit is performed during a cold start of the internal combustion engine system. The term "cold start" is a term well known in the art of internal combustion engines and refers in principle to all situations where the temperature of the engine is below the normal operating temperature, typically when the temperature of the engine cooling medium/water is below a certain level (e.g. 70 ℃). Determining the rotational friction of the rotating member and, if desired, the flushing/cleaning gas feed can be used as a routine measure which is always performed during cold start. In addition to it being a good routine for always checking and removing soot etc. in the gas feed at cold start, the EGR cooler generates more condensate when the engine is cold, so that if this condensate is used for flushing the gas feed, there may be a good flushing liquid supply during cold start. Alternatively, the routine measure at the time of cold start may be to perform flushing/cleaning without determining the rotational friction force of the rotating member in advance, or to perform flushing/cleaning even if the rotational friction force is lower than a threshold value.

The step of flushing the gas feed with a portion of the flushing liquid may also be performed during normal operation of the engine system, i.e. when the engine has reached its normal operating temperature. The engine system may be provided with a low temperature path or circuit for the cooling medium to also allow for the generation of a larger amount of condensate during normal operation of the engine system.

In one embodiment, the gas feed is configured to feed exhaust gas through a positive displacement pump (preferably a Roots-type blower having a pair of rotors with meshing lobes). Such pumps are suitable for feeding exhaust gases, but appear to be unreliable in this particular application if they are not regularly monitored for their function and various cleaning actions to remove soot and other deposits.

According to a second aspect, the invention relates to an internal combustion engine system configured to control any of the above-mentioned method steps.

According to a variant of the second aspect, the invention relates to a vehicle comprising an internal combustion engine system of the type described above.

According to a further aspect, the invention relates to:

a computer program product comprising program code means for controlling the steps of the above method when said program product is run on a computer;

a computer readable medium carrying a computer program comprising program code means for controlling the steps of the above method when said program product is run on a computer; and

a control unit for controlling an internal combustion engine system of the above-mentioned type, the control unit being configured to control the steps of the above-mentioned method.

Further advantages and advantageous features of the invention are disclosed in the following description.

Drawings

With reference to the accompanying drawings, the following is a more detailed description of embodiments of the invention, cited as examples.

In these figures:

figure 1 is a schematic view of a vehicle/truck provided with an internal combustion engine system according to the invention,

figure 2 is a schematic view of the internal combustion engine system according to figure 1,

FIG. 3 is a schematic cross-sectional view of a gas feed in the form of a Roots blower, and

fig. 4 is a flow chart of an exemplary embodiment of the method of the present invention.

Detailed Description

Fig. 1 shows a schematic view of a truck 1 provided with an internal combustion engine system 2 according to the invention.

Fig. 2 shows a schematic diagram of the internal combustion engine system 2 according to fig. 1. The engine system 2 is provided with an intake conduit 3, an exhaust conduit 4 and an Exhaust Gas Recirculation (EGR) system 5. The intake air 3a is compressed in a turbo compressor 3b before entering the intake conduit 3. The exhaust gas 4a leaves the schematically illustrated engine system 2 after having passed through an exhaust turbine 4b, which exhaust turbine 4b drives a turbine compressor 3b. The intake duct 3 guides air to a plurality of cylinders 21 (six in this example) arranged in the engine block 20, and the exhaust duct 4 guides exhaust gas away from the cylinders 21 and the engine block 21.

As with conventional engine systems, each cylinder 21 is provided with a piston (not shown) and intake and exhaust valves (not shown), wherein the pistons are connected to a crankshaft (not shown) which is further connected to the driving wheels of the vehicle 1 via various transmissions (not shown). The fuel supply and exhaust aftertreatment devices are not shown.

The EGR system 5 comprises an EGR conduit 6, which EGR conduit 6 fluidly connects the exhaust conduit 4 and the intake conduit 3. In order to provide an EGR flow when the pressure in the inlet conduit 3 is higher than the pressure in the outlet conduit 4, a gas feed 7 is arranged in the EGR conduit 6, which gas feed 7 is configured to feed exhaust gas from the outlet conduit 4 to the inlet conduit 3. In this example, the gas feeding means 7 is a Roots-type blower (see FIG. 3). The drive motor 9, in this case an electric motor, is arranged to drive the gas feeding means 7, which in this case means that the drive motor 9 is arranged to rotate the rotating members 71, 72 (see fig. 3) of the gas feeding means 7.

The EGR system 5 further includes: an EGR valve 12 for opening/closing the EGR conduit 6 (the gas feeding device 7 may also be used as an EGR valve, see below); an EGR cooling device 8 arranged to allow cooling of the exhaust gases flowing through the EGR conduit 6; an EGR bypass conduit 10 arranged in fluid communication with the EGR conduit 6 upstream and downstream of the gas feed means 7 so as to allow EGR flow bypassing the gas feed means 7; and a bypass valve 11 disposed in the EGR bypass conduit 10.

Fig. 2 further indicates an optional flushing liquid channel 13, which flushing liquid channel 13 is arranged to fluidly connect an optional flushing liquid tank 14 with the EGR conduit 6 upstream of the EGR gas feed means 7 for introducing flushing liquid into the EGR conduit 6. As will be described below, the channel 13 and the tank 14 may be used as an alternative or supplement to providing flushing liquid directly in the EGR duct 6 by condensation.

The engine system 2 further comprises a control unit (not shown) configured to control various parts and functions of the engine system 2 and to control, for example, all method steps described in the present disclosure. The control unit receives information from various sensors (not shown) arranged in the engine system 2. The principle function of a control unit for controlling the operation of an internal combustion engine and an engine system is well known in the art.

During normal operation of the engine system 2, the pressure in the inlet conduit 3 is higher than the pressure in the exhaust conduit 4, the EGR valve 12 is open, the bypass valve 11 is closed, and the gas feed 7 feeds exhaust gas from the exhaust conduit 4 to the inlet conduit 3 through the EGR conduit 6. The gas feed 7 may for example act as an EGR valve by closing itself and locking it in a fixed (non-rotating) position substantially preventing through-flow. This is done by controlling the electric drive motor 9. Thus, in this example, the EGR valve 12 is not necessary. When the gas feed 7 is closed and locked, the opening of the bypass valve 11 allows the exhaust gas flow through the EGR bypass conduit 10. The gas feed 7 may be closed but set in a mode allowing through-flow, i.e. allowing rotation of the

rotary members

71, 72 of the Roots blower.

Fig. 3 shows a schematic view of a gas feed 7 arranged in an EGR duct 6, wherein the gas feed 7 is in the form of a Roots-type blower having first and second

rotary members

71, 72, said first and second

rotary members

71, 72 being provided with

engagement lobes

71a, 71b, 72a, 72b configured to rotate within a peripheral housing 73. Roots-type blowers are known per se. In some Roots-type blowers, each rotating member is provided with more than two lobes. With respect to fig. 3, the incoming EGR flow in the EGR conduit 6 passes through the left inlet and is displaced (as indicated by the arrows) by the rotating

members

71, 72 to the right outlet and further into the EGR conduit 6 downstream of the gas feed 7 (towards the intake conduit 3 and the cylinders 21 as shown in fig. 1).

Fig. 4 shows a flow chart of an example of a method of operating the internal combustion engine system 2, in which an indication of accumulated deposits of soot, hydrocarbons or other pollutants in the gas feed device 7 is detected by determining whether the rotational friction of the

rotating members

71, 72 of the gas feed device 7 exceeds a threshold value. The example also illustrates which actions may be taken if the threshold is exceeded, and further includes the step of checking whether the action taken has already had the desired effect.

The example of fig. 4 includes the following steps:

s1-determining whether the rotational friction of the

rotating members

71, 72 of the gas feeding device 7 exceeds a threshold value by measuring the torque applied to the

rotating members

71, 72, measuring the actual rotational speeds of the

rotating members

71, 72, determining the rotational friction of the

rotating members

71, 72, and comparing the determined rotational friction with the threshold value;

and, if the threshold is exceeded in step S1, taking at least one of the following steps S2a-S2 d:

s2 a-operating the rotating

members

71, 72 in a reverse rotational direction opposite to the rotational direction used under normal operating conditions;

s2 b-increasing the driving power of the driving motor 9 arranged to drive the gas feeding means 7 and the

rotating members

71, 72 to a power level higher than the power level used under normal operating conditions;

s2 c-flushing and cleaning the EGR gas feed means 7 by providing flushing liquid in the form of EGR condensate in the EGR conduit 6 upstream of the EGR gas feed means 7; and/or

S2 d-increasing the temperature of the exhaust gas flowing through the gas feed means 7,

the following steps are:

s3-repeat step S1 to determine whether steps S2a-S2d have had the desired effect of "cleaning the gas feed 7 such that the rotational friction of the

rotating members

71, 72 has fallen below a threshold".

The actions after step S3 depend on the outcome of S3:

if it is determined in S3 that the rotational friction has decreased and fallen below the threshold value, it may be taken as an indication that the accumulated deposits have been removed, which means that the methods S1-S3 may be terminated and the engine system 2 may be returned to normal operating conditions (e.g. if the temperature of the exhaust gas or the power of the drive motor has increased, it may now be decreased to a normal level).

If it is determined in S3 that the rotational friction force still exceeds the threshold value, one or more of steps S2a-S2d may be performed again (possibly several times), followed by further repeating step S1 to check if the rotational friction force has fallen below the threshold value, and if not, one or more of steps S2a-S2d may be repeated again. If the rotational friction does not drop below the threshold value after a certain number or combination of cleaning operations, the engine system 2 may be controlled so as to i) close and lock the gas feed 7, ii) increase the pressure in the exhaust conduit 4 when needed (e.g. by using an engine brake, as described above), and iii) open the bypass valve 11 so as to introduce the exhaust flow in the EGR conduit 6 into the bypass conduit 10 and through the bypass conduit 10. Another option in this case is to close the EGR duct 6 (via the gas feed 7 or the EGR valve 12) and operate the engine system 2 without EGR. Yet another option is to shut down the entire engine system 2.

The rotational friction of the

rotating members

71, 72 of the gas feeding means 7 can be determined continuously, which means that steps S1 and S3 do not necessarily have to be separate steps starting and ending.

Step S2a may include pulsed counter-rotation and alternating directions, as further described above.

Step S2b may include a maximum power level and a threshold for a maximum period of time to operate at a higher than normal power level.

In the present example, step S2c is performed by operating the engine system 2 such that the EGR exhaust gas is condensed in the EGR cooling device 8 or downstream of the EGR cooling device 8. If a sufficient amount of EGR condensate is not being produced in step S2, this step may include an act of controlling the engine system 2 to produce more EGR condensate, such as by increasing the efficiency of the EGR cooling device 8, increasing the mass flow of exhaust gas through the EGR conduit 6, and/or increasing the fuel ratio in the air-fuel mixture combusted in the internal combustion engine system 2. Instead of or in addition to the provision of flushing liquid used in step S2c by directly producing EGR condensate in the EGR conduit 6, flushing liquid may be introduced into the EGR conduit 6 from the flushing liquid tank 14 via the flushing liquid channel 13. The flushing tank 14 may contain previously accumulated EGR condensate or another liquid.

Step S2d may include operating the internal combustion engine system 2 in a particular mode and/or reducing the cooling effect of the EGR cooler device 8, as further described above.

For steps S2a-S2b, no actual engine components of the engine system 2 have to be operated, i.e. the pistons do not have to be moved, any air has to be fed to the cylinders 21, any exhaust gases have to be generated, etc., because no exhaust gas flow through the EGR duct 6 is required. If rinse liquid is taken from the rinse liquid tank 14, step S2c does not require any EGR flow, but if no exhaust flow pushes the rinse liquid towards the gas feed 7 and through the gas feed 7, the cleaning effect may be small or negligible.

Two or more of these steps may be performed consecutively (immediately) and/or simultaneously, except that any cleaning step S2a-S2d may be repeated.

Regarding determining the rotational friction of the

rotating members

71, 72 of the gas feeding means 7, it may comprise one or more of the following steps:

measuring the torque applied to the

rotating members

71, 72;

measuring the drive power of the drive motor 9, for example the current of the drive motor;

-measuring the actual rotational speed of the

rotating members

71, 72;

measuring the response time of the

rotating members

71, 72 between the variation of the driving power and the resulting variation of the rotational speed.

As an example, the rotational friction force may be calculated or at least estimated from measurements of the applied torque and the actual rotational speed or from measurements of the drive power and the response time. Which threshold value is selected for the rotational friction depends on the particular application (e.g. on the type and size of the gas feed 7).

It should be understood that the invention is not limited to the embodiments described above and shown in the drawings; rather, it will be apparent to those skilled in the art that many modifications and variations are possible within the scope of the appended claims.

Claims

1. A method for operating an internal combustion engine system (2),

wherein the internal combustion engine system (2) is provided with an inlet conduit (3), an exhaust conduit (4) and an exhaust gas recirculation EGR system (5),

wherein the EGR system (5) comprises an EGR conduit (6), the EGR conduit (6) fluidly connecting the exhaust conduit (4) and the intake conduit (3), and wherein a gas feed (7) is arranged in the EGR conduit (6), the gas feed (7) being configured to feed exhaust gas from the exhaust conduit (4) to the intake conduit (3),

it is characterized in that the method comprises the steps of,

the method comprises the following steps:

-detecting an indication of accumulated deposits of soot, hydrocarbons or other contaminants in the gas feeding device (7) by determining whether the rotational friction of a rotating member (71, 72) of the gas feeding device (7) exceeds a threshold value, and

wherein the gas feed (7) is configured to feed exhaust gas through a positive displacement pump, which is a Roots blower, having a pair of rotors provided with meshing lobes (71 a, 71b, 72a, 72 b).

2. The method of claim 1, wherein the determination of rotational friction comprises one or more of:

-measuring the torque applied to the rotating member (71, 72);

-measuring the driving power of a driving source (9) arranged to drive the gas feeding means (7) and rotate the rotating member (71, 72);

-measuring the actual rotational speed of the rotating member (71, 72);

-measuring the response time of the rotating member (71, 72) between a change in driving power and a resulting change in rotational speed.

3. The method according to claim 1 or 2, wherein in case an indication of accumulated deposits is detected, the method further comprises the steps of:

-operating the rotating member (71, 72) in a counter-rotating direction opposite to the rotating direction used under normal operating conditions.

4. A method according to claim 3, wherein the rotating member (71, 72) is pulsed in the reverse rotation direction for a short period of time, wherein pulsed reverse operation is followed by continued operation in a normal operation rotation direction.

5. The method according to claim 4, wherein the short period of time the rotating member (71, 72) is running in the reverse direction is less than 10s.

6. The method according to claim 4, wherein the method comprises the steps of:

-repeating the step of pulsing the rotating members (71, 72) in a counter-rotating direction.

7. The method according to claim 4, wherein the method comprises the steps of: the rotating members (71, 72) are alternately operated in the reverse rotation direction and the normal rotation direction in a pulse manner.

8. The method according to claim 1 or 2, wherein in case an indication of accumulated deposits is detected, the method further comprises the steps of:

-increasing the driving power of a driving motor to a power level higher than the power level used under normal operating conditions, the driving motor being arranged to drive the gas feeding means (7) and the rotating member (71, 72).

9. The method according to claim 1 or 2, wherein in case an indication of accumulated deposits is detected, the method further comprises the steps of:

-directing the exhaust gas flow in the EGR conduit (6) into a bypass conduit (10), the bypass conduit (10) being arranged in fluid communication with the EGR conduit (6) upstream and downstream of the gas feed (7).

10. The method according to claim 1 or 2, wherein in case an indication of accumulated deposits is detected, the method further comprises the steps of:

-increasing the temperature of the exhaust gas flowing through the gas feed (7).

11. The method according to claim 10, wherein the method comprises the steps of:

-operating the internal combustion engine system (2) in order to raise the temperature of the exhaust gases and/or to reduce the cooling effect of an EGR cooler device (8) arranged in the EGR conduit (6) upstream of the gas feed device (7).

12. The method according to claim 1 or 2, wherein in case an indication of accumulated deposits is detected, the method further comprises the steps of:

-providing flushing liquid in the EGR conduit (6) upstream of the gas feed means (7) for flushing and cleaning the gas feed means (7).

13. The method of claim 12, wherein the method further comprises the steps of:

-condensing exhaust gases in an EGR cooler device (8) arranged in connection with the EGR conduit (6) or downstream of the EGR cooler device (8) in order to form an EGR condensate, and

-using the EGR condensate as the flushing liquid.

14. The method according to claim 12, wherein the step of providing the flushing fluid in the EGR conduit (6) is performed during a cold start of the internal combustion engine system.

15. An internal combustion engine system (2), the internal combustion engine system (2) being provided with an inlet conduit (3), an exhaust conduit (4) and an exhaust gas recirculation, EGR, system (5), wherein the EGR system (5) comprises an EGR conduit (6), the EGR conduit (6) fluidly connecting the exhaust conduit (4) and the inlet conduit (3), and wherein a gas feed device (7) is arranged in the EGR conduit (6), the gas feed device (7) being configured to feed exhaust gas from the exhaust conduit (4) to the inlet conduit (3), and wherein the gas feed device comprises at least one rotating member (71, 72),

it is characterized in that the method comprises the steps of,

the engine system (2) is configured to control the steps of the method of any of the preceding claims.

16. A vehicle (1) comprising an internal combustion engine system (2) according to claim 15.

17. A computer readable medium carrying a computer program comprising program code means for controlling the steps of the method of any one of claims 1 to 14 when said computer program is run on a computer.

18. A control unit for controlling an internal combustion engine system (2) according to claim 15, the control unit being configured to control the steps of the method according to any one of claims 1 to 14.